Context

MongoDBVectorSearch.delete Incorrectly communicates that passing in "ids" will appropriately delete documents when, in actually it deletes values by the text_key. This function needs to be refactored to be clearer and also allow for MongoDB ObjectIds to be deleted as well. We should also document the types we can take for delete. 
I.e. [str(ObjectId), ObjectId, \{"$oid": str(ObjectId)}] are all valid types

MongoDBVectorSearch.add_texts Returns a list of ObjectIds. Since the RAG Chain cannot serialize bson ObjectIds, we should return a list of dictionaries specified as `{"$oid": str(ObjectId) }`. 

Definition of done

Above functions have been refactored

Pitfalls

The changes to add_texts can be seen as breaking API changes so we may have to do a versioning bump.